This application is based upon and claims the benefit of priority from Korean Patent Application No. 2003-80094, filed on Nov. 13, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The invention relates to an optical recording and/or reproducing apparatus, and more particularly, to an ultra small, integrated optical pickup and an optical recording and/or reproducing apparatus using the same.
2. Description of the Related Art
In an optical recording (and/or reproducing apparatus) that records arbitrary information on an optical information storage medium (and/or reproduces information recorded on the optical information storage medium) by focusing laser light using an objective lens, the recording capacity is determined according to the size of a focused light spot. The size (S) of a focused light spot is determined according to the wavelength (λ) of laser light and the numerical aperture (NA) of an objective lens, as expressed by formula (1) below.S∝λ/NA  (1)
Therefore, to reduce the size of a light spot focused on an optical information storage medium, and thereby provide a higher recording density, research into an optical recording and/or reproducing apparatus using a short wavelength light source such as a blue laser and an objective lens having an NA of 0.6 or greater has been conducted.
Since the development of compact discs (CDs), which require light of a wavelength of 780 nm and an objective lens having an NA of 0.45 or 0.5 to record information thereon and/or reproduce information therefrom, intensive research has been conducted to raise the recording density and information storage capacity of the media. Digital versatile discs (DVDs), upon which information can be recorded on and reproduced from using light having a wavelength of 650 nm and an objective lens having an NA or 0.6 or 0.65, were obtained as a product of the research.
In current years, there has been steady progress in research into high-density information storage media using blue light having a wavelength of, for example, 405 nm, and a recording capacity of 20 GB or greater.
There have been efforts to standardize such high-density optical information storage media, and a few standards have almost been set up. For example, when light having a blue wavelength of 405 nm is used in a high-density optical information storage medium, an objective lens for this high-density optical information storage medium has an NA of 0.65 or 0.85, which will be described later.
A further difference between CDs and DVDs is that, while the thickness of a DVD is 0.6 mm, the thickness of a CD is 1.2 mm. This is because the tolerance to a tilt of the optical information storage medium should be ensured since a NA of an objective lens is increased to 0.6 for the DVD from 0.45 for the CD.
In a high-density optical information storage medium having a higher storage capacity than DVDs, when the NA of an objective lens therefore is increased to, for example, 0.85, the thickness of the high-density optical information storage medium has to be reduced to about 0.1 mm.
Such a high-density optical information storage medium that has a reduced thickness and requires a greater NA objective lens is referred to as a “blue-ray disc (BD)”. According to the standards for BDs, the wavelength of a light source is 405 nm, and the NA of an objective lens is 0.85. A standard thickness of the optical information storage medium for BDs is about 0.1 mm.
In addition to BDs, advanced optical discs (AODs) are currently under development as high-density optical information storage media. AODs have the same substrate thickness and require an objective lens having the same NA as for DVDs. However, the wavelength of a standard light source, a blue wavelength of, for example, 405 nm, matches the standard for BDs.
In addition to the requirement for reducing the size of a light spot with an objective lens having a greater NA for high-density, high-capacity optical information storage media, there is a need for a slimmer, smaller optical system constituting an optical pickup.
Along with the increasing need for using optical recording and/or reproducing apparatuses in portable terminals, such as personal digital assistants (PDAs), mobile phones, digital cameras, portable disc players, camcoders, etc., recently, there has been an increasing need for slim optical pickups. For applications in the field of portable terminals, optical pickups should be slim and small and be able to record and/or reproduce a large amount of information, such as music, moving pictures, etc., at a high density.
However, there are technical limitations in manufacturing a small, slim optical system by reducing the sizes of optical elements constituting a conventional optical pickup, such as those currently used in optical recording and/reproducing apparatuses for CDs and/or DVDs.
Furthermore, the conventional optical pickup is constructed by optically aligning and binding a plurality of individually manufactured optical elements. Therefore, due to an assembling error in the assembling and aligning of parts, the reliability of the assembled optical pick up, and the degree of automation, are lowered.